Evolution of Dust-Obscured Star Formation and Gas to z=2.2 from HiZELS

Abstract

We investigate the far-infrared properties of galaxies selected via deep, narrow-band imaging of the H$\hat{I}\pm$ emission line in four redshift slices from $z=0.40$--$2.23$ over $\sim 1$deg${}^2$ as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE bands, along with $850\hat{I}¼$m imaging from SCUBA-2 to study the evolution of the dust properties of H$\hat{I}\pm$-emitters selected above an evolving characteristic luminosity threshold, $0.2L_{\mathrm{H}\hat{I}\pm }^{\star }(z)$. We investigate the relationship between the dust temperatures and the far-infrared luminosities of our stacked samples, finding that H$\hat{I}\pm$-selection identifies cold, low-$L_{\mathrm{IR}}$ galaxies ($T_{\mathrm{dust}}\sim 14$k; $\log [L_{\mathrm{IR}}/{\mathrm{L}}_{\odot }]\sim 9.9$) at $z=0.40$, and more luminous, warmer systems ($T_{\mathrm{dust}}\sim 34$k; $\log [L_{\mathrm{IR}}/{\mathrm{L}}_{\odot }]\sim 11.5$) at $z=2.23$. Using a modified greybody model, we estimate "characteristic sizes" for the dust-emitting regions of HiZELS galaxies of $\sim 0.5$kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy ISM structure. Lastly, we measure the dust masses from our far-IR SEDs along with metallicity-dependent gas-to-dust ratios ($\hat{I}{´}_{\mathrm{GDR}}$) to measure typical molecular gas masses of $\sim 10^{10}$M${}_{\odot }$ for these bright H$\hat{I}\pm$-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of H$\hat{I}\pm$-selected galaxies, we find that typical star-forming galaxies brighter than $0.2L_{\mathrm{H}\hat{I}\pm }^{\star }(z)$ host a significant fraction ($35\pm 10$%) of the total gas content of the Universe, consistent with the predictions of the latest cosmological simulations.

17 pages, 4 figures, accepted for publication in The Astrophysical Journal